Logical multi-node applications are implemented using two or more network nodes/hosts and can provide a wide variety of services, such as different web applications, back office, document management, communications, etc. Logical applications can range from simple websites that use only a few nodes/hosts to more complex structures in terms of both scale and depth, which can use hundreds of thousands of different nodes/hosts.
Migration is the task of moving a virtual computing instance (VCI) from one physical hardware environment to another. Migration between different clouds or environments, or even smaller-scale migration within a datacentre, of VCIs that implement a logical multi-node applications can pose challenges, such as downtime. For example, an application comprising an email system may require at least one VCI that performs a database server role to be ready before a VCI performing a web server role starts to request data from it. If a web server role VCI attempts to request the data whilst the database server role VCIs are unavailable due to being migrated then this will result in errors, or at least degrade performance.